Stackable container comprising an arched base having a wide area of contact

ABSTRACT

Stackable container ( 1 ) having a body ( 2 ) and a bottom ( 3 ) comprising:
     an annular seat ( 10 ) defining a seating plane ( 11 ) complementary with a peripheral face ( 8 ) provided on a shoulder ( 4 );   a conical arch ( 14 ) that extends from the seat ( 10 ).
 
In this container:
   an outer transverse extension Dext of the seat and an overall transverse extension D of the body are such that:   

     
       
         
           
             
               Dext 
               D 
             
             ≥ 
             0.8 
           
         
       
         
         the arch ( 14 ) has a peripheral section ( 17 ) complementary with a frustoconical surface ( 7 ) of the shoulder ( 4 ), 
         the seating plane ( 11 ) and the peripheral support section ( 17 ) define a contact surface, the projection of which on the seating plane ( 11 ) has a surface area S C  such that: 
       
    
     
       
         
           
             
               Sc 
               S 
             
             ≥ 
             0.4 
           
         
       
     
     where S is the surface area delimited by an outer perimeter ( 12 ) of the seat ( 10 ).

The invention concerns containers, and more particularly stackable containers, that are shaped to be able to be stacked on each other, and having for that purpose a bottom and a neck that are substantially complementary so that the neck of one underlying container can be inserted into the bottom of an identical upper container.

Stackable containers are useful in numerous applications where the containers are not grouped together in small numbers (for example from six to eight containers for domestic use) then shrink-wrapped in packs, but rather are stacked directly on each other in order to be palletized; once the pallet is full, it can be shrink-wrapped.

Obviously, it is necessary to stabilize the containers as much as possible to keep the stacks from collapsing before final packaging. This involves the safety of the personnel concerned and the integrity of the containers.

The U.S. Pat. No. 7,699,171 (Consolidated Container Company) describes a substantially cube-shaped container with a capacity of between one pint (about 0.5 L) and five gallons (about 19 L), and preferably one gallon (about 3.8 L), the bottom of which defines a conical stacking repository defining a perimeter corresponding to the perimeter of a shoulder part of a container of identical structure.

The stacking method consists of manually grouping the containers into pairs, of shrink-wrapping each pair, then positioning the pairs thus established on a pallet. When a first layer of containers has been formed, a second layer of containers grouped and shrink-wrapped in pairs is stacked on the first layer, by interlocking the containers of the second layer on the top of those of the first layer.

A “locking” is achieved between an upper container and an identical lower container, and more specifically between a hollow part of the bottom of the upper container and the shoulder part of the identical lower container.

This “locking” does not appear to be clearly defined, although it is understood that it is achieved locally on the upper container at a hollow repository formed in (or adjacent to) the stacking repository, and on the lower container at a lip formed on the periphery of the shoulder part.

The containers described in this document, and their stacking technique—related to the shape of the containers—have several disadvantages.

Firstly, the distribution of loads is insufficient. More specifically, the surfaces in contact between the upper container and the identical lower container (bearing the loads due to the weight of the upper container and any containers that are placed thereon in the stack) are located near zones having sharp variations of curvature (typically a lip formed on the periphery of the shoulder part), likely to constitute incipient cracks.

Secondly, because of the shape and size of the zones (on the bottom and on the shoulder) that are intended to cooperate, the proposed interlocking does not have sufficient rigidity to allow free stacking of the containers. It is understandable that grouping and shrink-wrapping the containers in pairs is recommended in order to compensate for this lack of natural rigidity of the stack.

Thirdly, grouping and shrink-wrapping containers in pairs, which can be justified for palletizing large-capacity containers (typically the five-gallon containers described in the aforementioned patent), is not realistic for average- or small-capacity containers (typically one pint), for which the modern production rates, up to 50,000 containers per hour, are impossible to keep up with by the operators responsible for forming in pairs, shrink-wrapping and palletizing.

Fourthly, the centering of an upper container with respect to a lower container, essential for the recommended “locking,” requires a precise positioning of the containers during stacking, unless it is accepted that the containers be guided, sliding the neck of the lower container against the conical stacking repository of the upper container. Such guiding, which can cause shocks, can damage the conical stacking repository and/or the peelable lid closing the neck of the lower container.

Fifthly, even if it is acknowledged that the container can be of small capacity (one pint), it is difficult to see how to adapt the shape of the bottom of such a container to a wide neck (i.e., the neck of which is relatively wide with respect to the body of the container), thus reducing the available space at the shoulder.

Moreover, the document EP 0 698 557 describes stackable containers of rectangular cross-section, designed to localize the stacking loads at the corners of upper rectangular portions of the containers. However, the containers are dimensioned so that a space remains between their sloped surfaces and they are not in contact.

This technique has a major disadvantage: the recommended space between the conical surfaces, necessary for localizing the loads on the flat peripheral parts of the containers, results in a lateral play of positioning of the containers during stacking. This play, cumulative on a stack of three (or more) containers, makes the stack naturally unstable and thus susceptible to collapsing.

Consequently, a first objective is to propose a stackable container, the structure of which confers good structural rigidity on the stack in the absence of any packaging, particularly in view of allowing risk-free palletization.

A second objective is to propose a stackable container, the positioning of which on an identical underlying container is simple and easy.

A third objective is to propose a stackable container with high resistance to compression due to the stacking.

A fourth objective is to propose a stackable container providing good distribution of loads due to the stacking.

A fifth objective is to propose an easily stackable wide-neck container.

A sixth objective is to propose a stackable container fulfilling at least one of the aforementioned objectives while ensuring good blowability.

To that end, a stackable container of plastic material is proposed, comprising a body extending along a principal axis and having an overall transverse extension D, a shoulder in an upper side of the extension of the body, a neck in the extension of the shoulder, and a bottom in a lower side of the extension of the body, the shoulder comprising, beneath the neck, a frustoconical surface, and at its junction with the body, a peripheral face defining a support plane substantially perpendicular to the principal axis, said peripheral support face being separated from the frustoconical surface by an axial step, the bottom comprising:

-   -   an annular seat defining a seating plane complementary to the         peripheral support face and having an outer transverse extension         Dext;     -   a conical arch that extends from the seat towards a central         zone.         In this container:     -   the outer transverse extension Dext of the seat and the overall         transverse extension D of the body are such that:

$\frac{D_{ext}}{D} \geq 0.8$

-   -   the arch has a peripheral support section that is complementary         to the frustoconical surface of the shoulder, which extends         between the seat and a central disc suitable for receiving the         neck of an underlying container,     -   the seating plane and the peripheral support section of the arch         define a contact surface, the projection of which on the seating         plane has a surface area S_(C) such that:

$\frac{Sc}{S} \geq 0.4$

where S is the surface area delimited by an outer perimeter of the seat.

Tests have shown that such a design makes it possible to obtain good coaxiality of the stacked containers, to the benefit of the stability of the stack, and good distribution of the load transmitted by the upper containers to the lower containers, all while guaranteeing good blowability, necessary for industrial-scale production.

The following additional characteristics can be foreseen, alone or in combination:

-   -   the shoulder comprises an axial step separating the peripheral         support face from the frustoconical surface, and the bottom         comprises an axial internal annular cheek that is complementary         to the step.     -   a height H of the cheek and a width L of the seating plane are         such that:

$0.5 \leq \frac{L}{H} \leq 2$

-   -   the ratio between an inner transverse extension Dint and an         outer transverse extension Dext of the seat is such that:

$0.7 \leq \frac{Dint}{Dext} \leq 0.95$

-   -   the frustoconical surface has a horizontal angle of between 5°         and 40°;     -   the ratio L/H is about 0.65;     -   the ratio Sc/S is about 0.55;     -   the frustoconical surface is provided with stiffeners;     -   the bottom is provided with a central disc having stiffeners;     -   the disc has an inside diameter Dp, the ratio of which, to the         overall transverse dimension D of the body, is greater than or         equal to 0.4.

Other objects and advantages will be seen from the following description of embodiments, provided with reference to the appended drawings in which:

FIG. 1 is a side view showing a container of plastic material, according to a first embodiment;

FIG. 2 is a view in perspective from below of the container of FIG. 1;

FIG. 3 is a view in perspective, in larger scale, showing the bottom of the container according to detail III of FIG. 2;

FIG. 4 is a view similar to FIG. 2, showing a container according to a second embodiment;

FIG. 5 is a view in perspective, in larger scale, showing the bottom of the container according to detail V of FIG. 4;

FIG. 6 is a detailed cross-sectional view of the container of either of the embodiments of FIG. 2 or 4, shown placed on a flat surface;

FIG. 7 is a detailed partial cross-sectional view of two stacked identical containers, according to either of the embodiments of FIG. 2 or 4.

Represented in FIGS. 1 to 3, on the one hand, and 4 and 5, on the other hand, are two embodiments of a container 1 formed by stretch blowing from a preform of thermoplastic material such as PET (polyethylene terephthalate). Said container 1, particularly a bottle, typically has a capacity of 2 L, although this capacity could be reduced, without modifying the proportions of the container 1, for example to 0.1 L or increased up to 20 L.

The container 1 comprises a cylindrical body 2 (which can be of square cross-section, as in the embodiment of FIG. 1, or circular, as in the embodiment of FIG. 3), that extends along a principal axis X.

The body 2 is extended, at a lower side, by a bottom 3, and at an upper side opposite to the bottom 3, by a shoulder 4, which in turn is extended by a neck 5 defining a mouth. The neck 5 is fitted, for example by threading, to allow the removable attachment of a cap 6.

The body 2 has an overall transverse extension (i.e., measured in a plane perpendicular to the principal axis X) denoted D. (D is the measurement of the outside diameter of the body 2 when the container 1 is symmetrical in revolution as in the example illustrated in FIGS. 4 and 5, or the measurement of one side of the body 2 in cross-section when the body is square in cross-section.)

In the example shown, the container 1 has a wide neck 5, i.e., the diameter of the neck 5, denoted Dc, is greater than one-third of the overall extension D of the body 2.

The shoulder 4 forms a transition between the neck 5 and the body 2. The shoulder 4 comprises, beneath the neck 5, a frustoconical surface 7, the horizontal angle of which, denoted A, measured with respect to a plane perpendicular to the axis of the container, is between 5° and 40°, and preferably about 25°.

As illustrated in FIG. 6, the frustoconical surface 7 does not join the body 2, the shoulder 4 comprising an annular peripheral support face 8, which defines a support plane perpendicular (or substantially perpendicular) to the principal axis X and has a width L, measured transversely.

Said peripheral support face 8 is separated from the frustoconical surface 7 by a step 9 that extends axially, i.e., substantially parallel to the principal axis X of the container 1, or preferably, as in the example illustrated in FIG. 6, it forms a slight taper having a sharp angle at the top. Said angle at the top is for example between about 15° and 45° (typically, said angle at the top is about 20°). The height of the step 9, measured axially, is denoted H.

As can be seen in FIG. 6, the bottom 3 is shaped to receive the upper part (shoulder 4 and neck 5) of an identical underlying container 1, so as to enable the stacking of the containers 1.

More specifically, the bottom 3 is partially shaped to be complementary to the shoulder 4, so as to allow stacking by simple insertion of the shoulder 4 of the underlying container 1 into the bottom 3 of the upper container.

Thus, the bottom 3 comprises, firstly, an annular seat 10 that defines a continuous seating plane 11, complementary to the peripheral support face 8 of the shoulder 4, and it extends in a plane perpendicular to the principal axis X. The following notations are used:

-   -   S is the surface area delimited by an outer perimeter 12 of the         seat 10 (at a junction between the seating plane 11 and the body         2), i.e., the overall surface area of the bottom 3, projected in         the plane of the support face 8(parallel to the axis X of the         container 1), and     -   Dext is the outer transverse extension of the seat 10, measured         at the outer perimeter 12 thereof (Dext is the measurement of         the outside diameter of the seat 10 when the container 1 is         symmetrical in revolution as in the example illustrated in FIGS.         4 and 5),

Moreover, the annular seat 10 defines an axial inner annular cheek 13 that is complementary to the step 9, which extends axially from the seating plane 11 towards the interior of the container 1. The cheek 13 extends substantially parallel to the principal axis X (when the step 9 extends substantially parallel to the principal axis X), or as illustrated in FIGS. 6 and 7, preferably forms a slight taper substantially identical to the taper of the step 9, enabling the easy placement of one container 1 with respect to the other.

The inner transverse extension of the seat 10 is denoted Dint, measured at the cheek 13.

It will be noted that Dext and Dint are the respective measurements of the inside and outside diameters of the seat 10 when the container 1 is symmetrical in revolution as in the example illustrated in FIGS. 4 and 5.

The bottom 3 comprises, in the second place, a conical arch 14 that extends from the seat 10—and more specifically from an inner edge 15 of the step 9—towards a central zone of the bottom 3.

As can be seen in FIGS. 6 and 7, the arch 14 is in two parts, and comprises:

-   -   a central disc 16, one lateral wall of which extends         substantially axially, preferably with a slight taper (with an         angle of taper, denoted B, of between 10° and 20°, and         preferably about 15°), said disk 16 being shaped and dimensioned         to completely enclose the neck 5 of the underlying container 1,     -   a peripheral support section 17, complementary to the         frustoconical surface 7 of the shoulder 4 of the underlying         container 1, said peripheral section 17 extending between an         upper edge of the cheek 13 and a lower edge 18 (in this instance         rounded) of the central disc 16, the transverse extension of         which is denoted Dp, measured perpendicular to the axis X of the         container 1 (Op is a diameter in the case of a container 1 that         is cylindrical in revolution as illustrated in the example of         FIGS. 4 and 5).

Therefore, the peripheral section 17 has the same horizontal angle A as the frustoconical surface 7 (between 5° and 40°, and preferably about 25°).

The seating plane 11 has a width, measured perpendicular to the axis X, substantially equal to the width L of the support face 8.

For a container 1 with a wide neck 5, as shown, because of the play necessary for insertion, the central disc 16 has an inside diameter Dp whose ratio to the overall transverse dimension D of the body 2 is greater than or equal to 0.4, and for example about 0.5:

$\frac{Dp}{D} \geq 0.4$

and for example:

$\frac{Dp}{D} \cong 0.5$

As represented in FIG. 7, when the container 1 is stacked on an underlying container 1, the shoulder 4 of the underlying container 1 is inserted into the bottom 3 of the upper container 1:

-   -   the seating plane 11 of the upper container 1 is applied against         the peripheral support face 8 of the underlying container 1;     -   the step 9 of the underlying container 1 is inserted into the         cheek 13 of the upper container 1;     -   the peripheral section 17 of the arch of the upper container 1         is applied against the frustoconical surface 7 of the underlying         container 1.

The seating plane 11, the cheek 13 and the peripheral section 17 of the arch 14 jointly define a contact surface with the shoulder 4 of the underlying container 1. The surface area of the projection of this contact surface onto the plane of the peripheral support face 8 of the underlying container (i.e., onto the seating plane 11) is denoted Sc.

Moreover, the cheek 13 extends axially over a height substantially equal to the height H of the step 9.

The bottom 3 is dimensioned in the following way:

-   -   the ratio between the outer transverse extension Dext of the         seat and the overall transverse extension of the body is greater         than 0.7, and preferably greater than 0.8:

$\frac{Dext}{D} \geq 0.8$

and preferably:

$\frac{Dext}{D} \geq 0.85$

-   -   preferably, the ratio of the height H of the cheek 13 and the         width L of the seating plane 11 is between 0.5 and 2 (and         preferably about 0.55):

$0.5 \leq \frac{L}{H} \leq 2$

-   -   the ratio between the surface area S_(C) of the support surface         formed by the seating plane 11, the cheek 13 and the peripheral         section 17, on the one hand, and the surface area S of the area         delimited by the outer perimeter 12 of the seat 10, on the other         hand, is greater than 0.4 and preferably greater than 0.5 and         less than 0.65:

$\frac{Sc}{S} \geq 0.4$

and preferably:

$0.5 \leq \frac{Sc}{S} \leq 0.65$

In other words, S_(C) represents the surface area of the plane surface delimited externally by the outer perimeter 12 of the seat 10, with transverse dimension Dext, and internally by the projection in the seating plane 11 of the lower edge of the disc, of transverse dimension Dp.

The result of the architecture just described is better structural rigidity of the stack of containers 1 thus designed and a better distribution of the compression forces exerted on an underlying container, in particular due to:

-   -   the large size of the support surface (also called interface)         between the two stacked containers 1, which maximizes the         friction and increases the strength of the stack;     -   the offset of the seat 10 (and therefore of the peripheral         support face 8) towards the periphery of the container 1         (resulting from the value of the ratio DextD being close to 1)

$\frac{Dext}{D}$

-   -   the perpendicularity of the seating plane 11 with respect to the         axis X of the container and the squareness of the seat 10         (resulting from the value of the ratio

$\frac{L}{H}$

being close to 1), these two factors limiting the risk of tipping of a container 1 with respect to an underlying container 1;

-   -   the large size of the contact surface between the peripheral         section 17 of the arch 14 and the frustoconical surface 7 of the         underlying container 1, which makes it possible to center the         containers 1 more easily and more quickly during stacking.

According to a particular embodiment,

$\frac{L}{H}$

is equal to about 0.65,

$\frac{Sc}{S}$

is equal to about 0.55, and

$\frac{Dext}{D}$

is equal to about 0.85, constitutes a good compromise between the structural rigidity of the container (which should be maximized) and its blowability (which should also be maximized, but which can vary in inverse proportion to the rigidity).

Moreover, it is preferable to maintain the ratio between the inner transverse extension Dint and the outer transverse extension Dext of the seat 10 between 0.7 and 0.95:

$0.7 \leq \frac{Dint}{Dext} \leq 0.95$

The result is a smaller width L of the seating plane (compared to the overall transverse extension of the bottom 3), which favors the intrinsic stability of the container 1, whether it rests on a flat surface (represented by broken lines in FIG. 6) or on an underlying container 1 on which it is stacked (as in the example of FIG. 7).

Furthermore, it can be preferable to provide the frustoconical surface 7, as illustrated in FIG. 7, with stiffeners 19 in the form of radial ribs or grooves, for example in a regular star shape over the circumference of the frustoconical surface 7. Said stiffeners 19 increase the structural rigidity of the frustoconical surface 7 and limit its sag during the stacking of the containers 1.

Similarly, as illustrated in FIGS. 3 and 5, the central disc 16 is also provided with stiffeners 20 in the form of radial ribs or grooves, distributed in star shape around the circumference of the disc 16 from a center. Said stiffeners 20 give the disc 16 good strength and in particular avoid its misalignment during the stacking of the containers 1, which would have adverse consequences on the good alignment of said containers during their stacking. 

1. Stackable container of plastic material comprising a body extending along a principal axis and having an overall transverse extension D, a shoulder on an upper side of the extension of the body, a neck in the extension of the shoulder, and a bottom on a lower side of the extension of the body, the shoulder comprising, beneath the neck, a frustoconical surface, and at its junction with the body, a peripheral face defining a support plane substantially perpendicular to the principal axis, the bottom comprising: an annular seat defining a seating plane complementary to the peripheral support face and having an outer transverse extension Dext; a conical arch that extends from the seat towards a central zone; characterized in that: the outer transverse extension Dext of the seat and the overall transverse extension D of the body are such that: $\frac{Dext}{D} \geq 0.8$ the arch has a peripheral support section that is complementary to the frustoconical surface, which extends between the seat and a central disc suitable for receiving the neck of an underlying container, the seating plane and the peripheral support section of the arch define a contact surface, the projection of which on the seating plane has a surface area S_(C) such that: $\frac{Sc}{S} \geq 0.4$ where S is the surface area delimited by an outer perimeter of the seat.
 2. Container according to claim 1, characterized in that the shoulder comprises an axial step separating the peripheral support face from the frustoconical surface, and the bottom comprises an axial internal annular cheek that is complementary to the step.
 3. Container according to claim 2, characterized in that a height H of the cheek and a width L of the seating plane are such that: $0.5 \leq \frac{L}{H} \leq 2$
 4. Container according to claim 1, characterized in that the ratio between an inner transverse extension Dint and an outer transverse extension Dext of the seat is such that: $0.7 \leq \frac{Dint}{Dext} \leq 0.95$
 5. Container according to claim 1, characterized in that the frustoconical surface has a horizontal angle (A) of between 5° and 40°.
 6. Container according to claim 1, characterized in that the L/H ratio is about 0.65.
 7. Container according to claim 1, characterized in that the Sc/S ratio is about 0.55.
 8. Container according to claim 1, characterized in that the frustoconical surface is provided with stiffeners.
 9. Container according to claim 1, characterized in that the bottom is fitted with a central disc provided with stiffeners.
 10. Container according to claim 1, characterized in that the disc has an inside diameter Dp, the ratio of which, to the overall transverse dimension D of the body, is greater than or equal to 0.4. 